1. Field of the Invention
The present invention relates to a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus.
In the present specification, the electrophotographic image forming apparatus is directed to, for example, an electrophotographic copying machine, an electrophotographic printer such as an LED printer or a laser beam printer, an electrophotographic facsimile machine and an electrophotographic word processor.
The process cartridge makes at least one of charging means, developing means and cleaning means and an electrophotographic photosensitive member integrally into a cartridge which is detachably mountable to a main body of the electrophotographic image forming apparatus, or makes at least the developing means and the electrophotographic photosensitive member integrally into a cartridge which is detachably mountable to a main body of the electrophotographic image forming apparatus.
2. Related Background Art
Up to now, in an image forming apparatus using an electrophotographic image forming process, there has been applied a process cartridge system which makes the electrophotographic photosensitive member and process means that operates on the electrophotographic photosensitive member into a cartridge which is detachably mountable to a main body of the electrophotographic image forming apparatus. The process cartridge system can remarkably be improved in the operability since the maintenance of the apparatus can be conducted by a user per se not depending on a service man. For that reason, the process cartridge system has been widely employed in the electrophotographic image forming apparatus.
In the electrophotographic image forming apparatus of the above process cartridge system, a user replaces the cartridge mounted on the apparatus by a fresh one. Therefore, it is a great convenience to provide the electrophotographic image forming apparatus with a function of informing the user that a developer within the process cartridge is completely depleted.
FIG. 13 shows an example of a conventional image forming apparatus A on which a process cartridge B is mounted. A developing device 9 which constitutes developing means by a process cartridge B includes a developing chamber 9A which supplies a developer T to a latent image formed on a photosensitive drum 7 and visualizes the latent image and a developer container 11A that contains the developer T therein. The developer T within the developer container 11A is fed to the developing portion 13 from the interior of the developing chamber 9A by the gravity and an agitating device 9e or other developer feeding means.
In the developing chamber 9A, a developing roller 9a that serves as a cylindrical developer bearing member for feeding the developer T up to a developing position opposite to the photosensitive drum 7 is disposed in the vicinity of the photosensitive drum 7. The developer T is attracted and held on the surface of the developing roller 9a, and the developer T is fed up to the developing position opposite to the photosensitive drum 7 due to the rotation of the developing roller 9a. 
The amount and height of the developer T are regulated and uniformly coated on the developing roller 9a by developer regulating means 9d such as a doctor blade while the developer T is being fed.
The developer T is rubbed by the developing roller 9a, the developer regulating means 9d or the developer T per se so as to be electrically charged during a process where the developer T is fed onto the developing roller 9a. 
Then, the developer T which has been fed to a portion of the developing roller 9a opposite to the photosensitive drum 7, that is, to a developing position by the developing roller 9a is transferred onto the photosensitive drum 7 due to an appropriate developing bias voltage applied between the photosensitive drum 7 and the developing roller 9a by a developing bias power supply 54 which serves as bias applying means, and an electrostatic latent image on the photosensitive drum 7 is then developed to form a toner image.
The developer T which has not been used for development is fed while it remains on the developing roller 9a, and then permitted to be again contained in the developing portion.
On the other hand, a recording medium 2 set in a sheet feed cassette 3a is conveyed to a transfer position by a pickup roller 3b, a pair of conveying rollers, a registration roller (not shown) and so on in synchronism with the formation of the toner image. A transfer roller 4 is disposed as transfer means at the transfer position, and the toner image on the photosensitive drum 7 is transferred onto the recording medium 2 by application of a voltage.
The recording medium 2 onto which the toner image has been transferred is conveyed to fixing means 5. The fixing means 5 includes a fixing roller 5b having a heater 5a therein and a driving roller 5c, and applies a heat and a pressure to the recording medium 2 which is passing through the fixing roller 5b to fix the transferred toner image onto the recording medium 2. Thereafter, the recording medium 2 is discharged to the external.
The photosensitive drum 7 from which the toner image has been transferred onto the recording medium 2 by the transfer roller 4 is subjected to a succeeding image forming process after the developer remaining on the photosensitive drum 7 has been removed by cleaning means 10. The cleaning means 10 scrapes off the residual developer on the photosensitive drum 7 by an elastic cleaning blade 10a disposed so as to be abutted against the photosensitive drum 7 and collects the residual developer thus scrapped off into a waste developer reservoir 10b. 
As described above, in the developing device 10, the developer T is depleted every time the developing operation is repeated. And if the developer is short, there may occur a defect such as a deterioration of the image density or a lack of the image. For that reason, it is necessary to monitor the presence/absence of the developer T in the developing chamber 9A and the develop container 11A so as to prevent the shortage of the developer T.
Under the above circumstances, the conventional developing device 9 includes a developer amount detecting device as means for detecting the residual amount of the developer. The developer amount detecting device includes a bar-shaped antenna electrode 35 for detection of the residual amount of the developer which is disposed horizontally in the interior of the developing chamber 9A as a member for the electrode to detect the residual amount of the developer T.
The developer amount detecting device further includes a developer amount measuring circuit 50. The developer amount measuring circuit 50 is equipped with a capacitance detecting circuit 52 as means for measuring a capacitance between the antenna electrode 35 and the developing roller 9a. The capacitance detecting circuit 52 is connected with the antenna electrode 35. With this structure, the developing bias voltage which is applied to the developing roller 9a by the developing bias power supply 54 is detected by the antenna electrode 35 to measure the capacitance between antenna electrode 35 and the developing roller 9a. 
The developer amount measuring circuit 50 also includes a reference capacitance 53 as means for setting a capacitance which is a reference for comparison and a capacitance detecting circuit 51 as means for measuring the reference capacitance 53. The reference capacitance 53 and the developing bias power supply 54 are connected to each other, and the developing bias voltage is detected through the reference capacitance 53, to thereby obtain the capacitance which is a reference in measurement of a unknown capacitance.
The developer amount detecting device compares an output of the capacitance detecting circuit 51 with an output of the capacitance detecting circuit 52 for the reference capacitance by a comparing circuit 55 serving as comparing means to detect a difference therebetween. Then, the developer amount detecting device judges the developer amount as the depletion of developer T by a developer amount warning circuit 57 and notifies the user that the developer T is little if the difference is lower than a given value.
The above system is mainly employed in a small-sized image forming apparatus on which the process cartridge is mounted since the system is simple in structure and inexpensive.
However, as described above, in the conventional image forming apparatus, the antenna electrode 35 is disposed within the developing chamber 9A. Therefore, this detecting method can detect a time immediately when the developer is completely depleted with a high accuracy (near-end detection). However, the amount of developer could not be successively detected.
The conventional developer amount detecting device is so designed as to detect the presence/absence of the developer within the developer container. That is, the conventional developer amount detecting device can merely detect that the developer is little immediately before the developer within the developer container has been completely depleted. In other words, the device could not detect the remaining amount of developer within the developer container.
On the other hand, if the remaining amount of developer within the developer container can be successively detected, the user can be informed of the developer depleted state within the developer container so that the user can prepare a fresh process cartridge at a replacing timing. This is very convenient for the user.
In order to solve the above problem, there has been proposed a developer remaining amount detecting method based on a pixel counting system in which the depleted amount of developer is calculated in accordance with the number of dots drawn by a laser. However, in this method, the depleted amount of developer to be detected is different between a graphic pattern and a text pattern. For that reason, in the case where the lifetime of the process cartridge is short to the degree of 3000 to 5000 sheets, the method is effective because an error in calculation is small. However, in the case where the lifetime of 10000 sheets or more is satisfied, a fear that the error in calculation becomes large in the latter half of the lifetime because of a difference in the depleted amount of developer due to the pattern is presumed.
FIG. 11 shows a state in which the developer is borne on the text pattern and the graphic pattern (solid image) as a schematic diagram showing the depleted amount of toner. This figure shows that the depleted amount of developer (toner) per one dot in the text pattern is more than that in the graphic pattern. FIG. 56 shows how the developer is decreased in the case where only the text pattern and only the graphic pattern are printed on 10000 sheets, respectively. It is understood from the figure that an error in calculation with respect to the pattern of the pixel count system is about xc2x110% in the lifetime of 10000 sheets of the process cartridge which is filled with toner of 500 g. That is, in the larger-capacity process cartridge, an improvement is further required to successively and accurately detect the remaining amount of developer.
An object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are capable of successively detecting the amount of developer.
Another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are capable of detecting the amount of developer with accuracy.
Still another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are capable of properly informing a user of the amount of developer.
Yet still another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus each having a plurality of developer remaining amount detecting means for successively detecting a developer remaining amount within a developer container in which the developer remaining amounts detectable by the respective developer remaining amount detecting means are overlapped with each other, and values detected by the respective developer remaining amount detecting means are weighted, respectively.
Yet still another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are capable of indicating a developer remaining amount more preferably for a user by shifting from a detected value of a first developer remaining amount detecting means to a detected value of a second developer remaining amount detecting means on the basis of a relation between regions detectable by the plurality of developer remaining amount detecting means and an error in detection in an appropriate method.
Yet still another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are capable of using a developer without adversely affecting an image, without troubling a user and without any uselessness.
Yet still another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are inexpensive, each having a developer amount detecting device with a simple structure which is capable of detecting a developer full state to a near-end state which is immediately before printing becomes defective even if the developing device or the process cartridge is long in lifetime with a more accuracy and with a high precision, and which are capable of further improving convenience when the user employs the device.
Yet still another object of the present invention is to provide a developer amount detecting method, a developing device, a process cartridge and an electrophotographic image forming apparatus which are inexpensive, each having a developer amount detecting device which is capable of monitoring a depleted state of the developer with accuracy and grasping a replacement timing of the developing device or the process cartridge with accuracy even if a plurality of users employ the device or a large-scaled print job is conducted, and which are capable of further improving convenience when the user employs the device.